1. Field of the Invention
The invention relates to a method for detecting the exact contour of targeted treatment areas, in particular, the external contour, i.e. mapping surgical target site contours precisely, especially the outer contour thereof.
In lesion surgery, use is made of invasive or non-invasive (radiation therapy) methods, in which it is principally desirable to be aware of the precise outer contours of the lesion so as to avoid disturbing healthy tissue surrounding the lesion during surgery. It is particularly important in the case of brain surgery to precisely distinguish between healthy and diseased tissue in deciding implementation invasive or non-invasive.
2. Description of Prior Art
Computer-assisted surgery has recently become popular, whereby surgical target site data is mapped by means of CT or MRI tomography and a referencing method, stored as slice images for various mapping planes and made available to the surgeon via a computer system and a display monitor.
In accordance with the methods used to date the surgeon in preparing for the operation marks the lesion requiring surgery or its contour in each slice plane with the aid of a display cursor. Marking is done manually for each of the slice planes in sequence, i.e. in each of three directions standing perpendicular to the other so that from the information provided as a whole the three-dimensional configuration of the lesion can be computed. It is with this information as to the configuration and location of the lesion that computer-assisted surgery can then be undertaken, the outer contour, i.e. distinguishing healthy surrounding tissue being particularly important in this respect.
The main drawback of this conventional method of marking the contour is its relative inaccuracy, due not only to the marking being done manually but also attributable to other unavoidable factors.
Thus, on the one hand, in the images displayable on the computer the transitions between healthy and diseased tissue are often quite unclear or blurred and accordingly hardly discernible to the naked eye. whilst. on the other, it may be that a healthy structure is just located in the surroundings of the diseased tissue which furnishes the same color or gray scale value as the diseased tissue in the computer display. It is particularly in the latter case that making a distinction between the two with the naked eye is very difficult or even impossible and there is thus the risk that marking lacking sufficient precision is to the detriment of healthy tissue in the operation on the basis of the marking data. Particularly in the brain quite natural changes in density exist in many locations which detriment or even make it impossible to detect the outer contour of lesions as described above.